Understanding the genetic and environmental mechanisms that underlie individual differences in general and specific mathematics cognition has important implications for mathematics education and prevention of specific learning disabilities in mathematics. The proposed research will provide the first systematic genetic investigation of individual differences in early mathematics learning and disabilities as well as the links among mathematics, reading, other cognitive abilities, motivation, and the environment. The proposed three-year project will capitalize on two ongoing twin studies - one in the U.S. and one in the U.K. - by testing the twins in their homes on diverse processes of mathematics learning. The U.S. study includes a representative sample of 350 same-sex twin pairs born between 1996 and 1998 who are being assessed longitudinally at three measurement occasions from kindergarten through third grade on a broad battery of measures of reading, cognitive skills, and family environmental factors. Examining these 700 children in their homes at eight years of age on a battery of mathematics measures will determine the role of genetic and environmental influences on individual differences in the normal range of mathematics development and links to reading and cognition. The U.K. study has investigated 7,500 twin pairs on language and cognitive development at two, three, four, and seven years of age, with ongoing testing at nine years of age, which includes teacher assessments of mathematics and reading based on the U.K. National Curriculum criteria at seven and nine years of age. Data from these 15,000 children will be used to select 350 twin pairs in which at least one child is in the lowest 5% of teacher assessments after exclusions. Assessing these 700 children in their homes at ten years of age on a battery of mathematics measures will assess the role of genetic and environmental influences on mathematics disabilities and their links to reading and cognition. DNA has been obtained on these children, which will provide a resource for future molecular genetic analyses. In addition to investigating genetic and environmental influence in mathematics abilities and disabilities, the proposed research will bring a multivariate genetic approach to bear on the vexed issue of general and specific mathematics abilities and disabilities. Developing a more informative model of how genes and environments work together to affect general and specific mathematics development has important implications on how to foster mathematics development as well as to detect, ameliorate and prevent problems.